The research projects in this proposed Asthma and Allergic Diseases Centers Grant all deal with the study of basic mechanisms relevant to expression of the atopic response. The methods employed have, with few exceptions, been developed and evaluated extensively in previous clinical studies. The titles of the three projects are: 1. Evaluation of Thymus Dependent Immune Function in Patients with Atopic Diseases and in Patients with Extreme Hyperimmunoglobulinemia E and Undue Susceptibility to Infection. 2. Evaluation of Immune Effector Systems in Patients with Extreme Hyperimmunoglobulinemia E and Undue Susceptibility to Infection. 3. An Evaluation of the Genetic Control of Allergen Sensitization in Atopy.